1. Field of the Invention
This invention relates to coating surgical fibers or surgical braids and, more particularly, to using dual capillaries to coat surgical fibers or braids to achieve unexpected results as evidenced by unexpectedly favorable reductions in the value of the coefficient of friction.
2. Related Art
A suture is used to sew tissue together, often during surgery. Often, the suture is comprised of a filament and a coating around the filament. The filament may be a monofilament-type or a braid-type.
The coating around a filament is critical to the performance of the suture. Specifically, an evenly coated fiber insures predictable and repeatable performance of the suture in surgery. As a length of suture is pulled through tissue, a certain amount of tissue drag is experienced. Excessive tissue drag can cause trauma to the tissue, and is therefore undesirable. The coefficient of friction of a suture is directly proportional to tissue drag and is an indicator of an evenly coated fiber. An evenly coated fiber has a lower coefficient of friction; an unevenly coated fiber has a higher coefficient of friction.
To determine generally whether a particular suture has a predictable even coating, the coefficient of friction is tested for a large number of suture samples. As shown in FIG. 1, test results indicating the coefficient of friction for multiple sample of sutures are illustrated. The reference suture in FIG. 1 is a coated suture currently available to the public. The non-coated fiber in FIG. 1 is a polybutester filament. The coated fiber referred to in FIG. 1 refers to a coated suture also available to the public. FIG. 1 illustrates that coated fibers such as the reference suture and the coated fiber generally provide improved performance, as well as predictable and repeatable performance as reflected in the coefficient of friction values, over non-coated filament. Accordingly, coated surgical sutures are often preferred over non-coated surgical sutures.
FIG. 2 illustrates coefficient of friction values for non-coated surgical filaments of size 7-0 and coated surgical fiber of size 7-0. As is evident from FIG. 2, the mean and the median coefficient of friction of the coated fiber is significantly lower than the mean and median coefficient of friction of the non-coated surgical fiber. However, it is also evident that the coated surgical fiber shows a large variation in the coefficient of friction among the samples tested. Variation in the coefficient in friction among various samples, especially a large variation, is an indication that the coating is applied unevenly and/or sections of surgical suture are not being coated. For example, the data points for coated surgical fibers within the coefficient of friction range of 7.5 to 8.2 indicate or strongly suggest that there has been some failure to uniformly coat the surgical fiber.
The coated surgical fibers (or surgical sutures) referred to in FIGS. 1 and 2 were coated using a single capillary process. In particular, a capillary tube is provided with a source of polymer coating material generally in the form of a polymer-in-solvent solution. A non-coated filament is then drawn across the capillary tube. As the filament is drawn across the capillary tube, a polymer-in-solvent solution is deposited on the surgical suture. When the solvent evaporates, only the polymer is left coating the filament.
Should an air bubble enter the capillary tube, a volume of polymer-in solvent solution would be displaced. Accordingly, as the fiber is drawn across the tube, the air bubble in the tube would be drawn towards the fiber until ultimately, the filament would come into contact with the air bubble and a portion of the filament in contact with the air bubble would remain uncoated for the length of time it takes or the air bubble to pass. Other potential sources of uneven coating include when the volume of polymer-in-solvent solution from the capillary tube is deposited unevenly on the filament.
Accordingly, there is a need in the art to provide a process for coating a filament which will produce a coated surgical suture which insures predictable and repeatable performance by being coated evenly.
There is a further need in the art to provide a process for coating a filament for a surgical suture which has a coated coefficient of friction which is consistently lower than that currently taught in the art.